In recent years, there has been development of organic semiconducting (OSC) materials in order to produce more versatile, lower cost electronic devices. Such materials find application in a wide range of devices or apparatus, including organic field effect transistors (OFETs), organic light emitting diodes (OLEDs), organic photodetectors (OPDs), organic photovoltaic (OPV) cells, sensors, memory elements and logic circuits to name just a few. The organic semiconducting materials are typically present in the electronic device in the form of a thin layer, for example of between 50 nm and 1 μm thickness.
The photosensitive layer in an OPV or OPD device is typically composed of at least two materials, a p-type semiconductor such as a polymer, an oligomer or a define molecular unit and a n-type semiconductor such as a fullerene derivative, graphene, a metal oxide, or quantum dots. In recent years, many p-type semiconductors, mainly polymers, have been prepared to enhance the performance of an OPV device. In comparison, the development of n-type semiconductor has been limited to only a few selected candidates.
Novel n-type semiconductors as promising alternative to PCBM-C60 fullerene are limited. FIG. 1 shows some known fullerene derivatives, including Fullerene F1 and the respective multiple adducts both described in WO2008/018931 and WO2010/087655, Fullerene F2 and the respective multiple adducts both described in U.S. Pat. No. 8,217,260, Fullerene F3 described in JP 2012-094829, Fullerene F4 described in WO 2009/008323 and JP 2011-98906 and Fullerene F5 and the respective multiple adducts both described in JP 2011-181719. However, the physical properties of these fullerene derivatives, such as solubility, light stability and thermal stability, are limiting their use in commercial applications.
OPV devices containing a derivative of Fullerene F2, namely the mono- and bis-indene-C60 fullerene as described in U.S. Pat. No. 8,217,260, have been reported to show increased power conversion efficiency (PCE) through open circuit voltage (Voc) increase while maintaining similar short circuit potential (Jsc) to equivalent devices with PCBM-C60 using P3HT as donor polymer to form the bulkheterojunction (BHJ). However, the mono-indene fullerene solubility is limited, resulting in poor coating quality, thus limiting the industrial use of the compound, while the bis-indene fullerene multicomponent mixture is not suited for amorphous polymers resulting in poor BHJ morphology and thus poor Jsc.
Thus there is still a need for fullerene derivatives which are easy to synthesize, especially by methods suitable for mass production, show good structural organization and film-forming properties, exhibit good electronic properties, especially a high charge carrier mobility, a good processability, especially a high solubility in organic solvents, and high light and thermal stability.
It is an aim of the present invention to provide fullerene derivatives that provide one or more of the above-mentioned advantageous properties. Another aim of the invention is to extend the pool of n-type OSC materials available to the expert. Other aims of the present invention are immediately evident to the expert from the following detailed description.
The inventors of the present invention have found that one or more of the above aims can be achieved by providing substituted indene fullerenes of formula I as disclosed and claimed hereinafter.
Surprisingly it is found that these fullerenes demonstrate one or more of the improved properties as described above, especially for use in OPV/OPD applications, compared to the fullerenes disclosed in prior art. Besides, these fullerenes as disclosed and claimed hereinafter can also be used as semiconductors in other electronic devices like OFETs or OLEDs.
Only few mono- or bisindene fullerenes have been reported in prior art until now. The substituted monoindene C70 fullerene A as shown in FIG. 2 has been reported in Chem. Commun., 2012, 48, 7616-7618, while a monoindene C60 with a exocyclic double bond at the 2 position (fullerene B) as shown in FIG. 2 has been reported in Org. Lett., 2013, 15, 4030-4033. However, it has neither been disclosed nor suggested that these fullerenes can lead to BHJ OPV devices with improved thermal and/or light stability compared to PCBM-C60.
Thus, until now substituted indene fullerenes have not been considered as potential replacement from PCBM type fullerene in the OPV or OPD device active layers nor for use as p-type or n-type semiconductors in OFET or OLED devices.